The field of the invention relates inhibiting the high temperature corrosivity of petroleum oils through the use of certain substituted aromatic acids.
Whole crudes and crude fractions with acid, including high organic acid content such as those containing carboxylic acids, (e.g., naphthenic acids), are corrosive to the equipment used to distill, extract, transport and process the crudes. Solutions to this problem have included use of corrosion-resistant alloys for equipment, addition of corrosion inhibitors, or neutralization of the organic acids with various bases.
The installation of corrosion-resistant alloys is capital intensive, as alloys such as 304 and 316 stainless steels are several times the cost of carbon steel. The corrosion inhibitors solution is less capital intensive; however costs can become an issue.
The effectiveness of phosphorus compounds against corrosion was discovered in 1906 (Coslett, British Patent 8,667 for phosphoric acid), and the use of these compounds is well known for aqueous systems.
Additionally, organic polysulfides (Babaian-Kibala, U.S. Pat. No. 5,552,085), organic phosphites (Zetlmeisl, U.S. Pat. No. 4,941,994), and phosphate/phosphite esters (Babaian-Kibala, U.S. Pat. No. 5,630,964), all of which have been claimed to be effective in a hydrocarbon-rich phase against naphthenic acid corrosion. However, their high oil solubility incurs the risk of distillate sidestream contamination by phosphorus. Furthermore, there is also concern for potential downstream impact of phosphorus, such as the possibility of catalyst poisoning by phosphorus-containing compounds, and concerns for downstream units. Mitigation options that use phosphorus and sulfur-free compounds, either in a refinery pipestill or in subsequent downstream process units, are also desirable since entrained phosphorus contamination in distillate sidestreams can result in downstream catalyst deactivation and/or product quality problems. These concerns preclude addition of such inhibitors to sidestreams subjected to catalytic processing. Also, since phosphorus can concentrate in the residuum, processing or product options for the latter may become limited. Any addition of sulfur from the inhibitor also requires subsequent processing for their removal as these may contribute to environmental burdens or product instability. Parahydrocarbyl-substituted phenol or thiophenol dicarboxylic acids have been reported as anti-corrosion and anti-rust additives in liquid hydrocarbon fuels and lubricants used in internal combustion engines (Strang U.S. Pat. No. 3,730,485). However, their formulas specifically require a para hydrocarbyl group in addition to the three acidic functionalities on the aromatic ring. In a formulated oil, these additives would be exposed to engine temperatures not exceeding 200xc2x0 C. Fused ring compounds having specifically hydroxy, carboxylic acid, and hydoxyalkyl groups have also been reported as having corrosion inhibition properties (Lawson, U.S. Pat. No. 5,258,532) but were applied to aqueous systems.
There remains a continuing need to develop additional options for mitigating the corrosivity of acidic crudes which are low cost, compatible with downstream processes and with product quality requirements. Applicants"" invention addresses these needs.
The acidic functionalities are preferably acidic xe2x80x94OH and/or xe2x80x94COOH groups. These additives are sulfur and phosphorus free.
An embodiment of the present invention is a method for inhibiting high temperature corrosion of corrosion prone metal surfaces caused by organic, typically naphthenic acids in petroleum streams by providing the metal surface with an effective, corrosion-inhibiting amount of certain aromatic compounds tri-substituted with acidic functionalities on the aromatic ring said functionalities are selected from xe2x80x94OH and xe2x80x94COOH groups. These triacids are selected from 5-hydroxyisophthallic acid and 1,3,5-benzenetricarboxylic acid, and 1,2,3-benzenetricarboxylic acid.
Another embodiment of the invention is a method to inhibit the high temperature corrosivity of an organic acid-containing petroleum stream or oil by providing a corrosion prone metal-containing surface to be exposed to the acid-containing petroleum stream with an effective, corrosion-inhibiting amount of the specified inhibitors/additives. The providing of the inhibitor may be carried out in the presence of the acid-containing petroleum stream and/or as a pretreatment of the corrosion prone metal surface before exposure to the acid-containing petroleum stream. Another embodiment provides for the products produced by the processes herein.
The present invention may suitably comprise, consist or consist essentially of the elements or steps disclosed and may be practiced in the absence of an element or step not disclosed.
Some petroleum streams, including petroleum oils, contain acids, including organic acids, such as naphthenic acids, that contribute to high temperature corrosion of internal surfaces of refinery equipment. Organic acids generally fall within the category of naphthenic and other organic acids. Naphthenic acid is a generic term used to identify a mixture of organic carboxylic acids present in petroleum stocks. Naphthenic acids may be present either alone or in combination with other organic acids, such as phenols. Naphthenic acids alone or in combination with other organic acids can cause corrosion at high temperatures in non-aqueous or essentially non-aqueous (hydrocarbon) environments, i.e., at temperatures ranging from about 200xc2x0 C. (329xc2x0 F.) to 420xc2x0 C. (790xc2x0 F.). Inorganic acids also may be present. Inhibition of corrosion due to the organic acid content of such petroleum streams, is desirable in order to increase the corrosion resistance, and thus useful life of internal (i.e., tube-side surfaces of reactors and other equipment having an external or shell-side and an internal or tube-side) metal surfaces of refinery equipment that are high temperature corrosion prone and are to be exposed to organic acid-containing petroleum stream at process conditions that result in high temperature corrosion of such internal surfaces. Mitigation options that use sulfur and phosphorus-free compounds as additives or inhibitors are advantageous since the presence of phosphorus and sulfur can affect downstream catalysts and/or product quality. Examples of such equipment include heat exchanger surfaces, pipestill vessels, transfer lines and piping, and pumps.
Petroleum streams that can be treated herein are any organic acid-containing petroleum streams, including whole crudes and crude oil fractions. As used herein, the term whole crudes means unrefined, non-distilled crudes.
Examples of metal surfaces that may benefit from treatment are any ferrous metals, such as carbon steel, and iron alloys.
The acidic aromatic species that may be used as inhibitors/additives are aromatic triacids, that is aromatic rings tri-substituted with acidic functionalities selected from xe2x80x94OH and xe2x80x94COOH groups. These additives/inhibitors are selected from 5-hydroxyisophthalic acid, 1,3,5-benzenetricarboxylic acid, and 1,2,3-benzenetricarboxylic acid.
Treatment temperatures will preferably range from about ambient to typically about 450xc2x0 C., preferably up to 350xc2x0 C.
The inhibitor is introduced in either a batch or continuous process to untreated (unadditized) petroleum oil. Additionally or separately, the metal surface may also be preconditioned by adding to a low acidity petroleum oil an amount of additive/inhibitor effective to inhibit corrosion in the organic acid containing petroleum oil to be treated before combination with the petroleum stream containing organic acids, and blending them by techniques known in the industry. Additional effective amounts may be introduced into the organic acid-containing petroleum stream itself as needed to maintain corrosion inhibition. Desirably, a continuous dosing of inhibitor to achieve and maintain the recommended effective level of corrosions inhibition is delivered. Thus, the additive/inhibitor may be introduced to the hydrocarbon rich environment or phase and/or to the metal surface itself.
The inhibitor is added in effective amounts, typically up to a total of 1000 wppm, more typically an effective amount of from about 10-100 wppm. The amount or concentration to be used is determined based on the acidity of the petroleum stream and the desired degree of corrosion inhibition needed. Typically, a reduction corresponding to at least forty (40) percent corrosion rate reduction can be achieved.
The effectiveness of corrosion inhibition is typically estimated in the laboratory by weight loss of metal coupons exposed to organic acids with and without the additive/inhibitor present. The relative decrease in metal weight loss due to the presence of corrosion inhibitor is a measure of the effectiveness of corrosion inhibition.
Naphthenic acid concentration in crude oil is determined by titration of the oil with KOH, until all acids have been neutralized. The concentration is reported in Total Acid Number (TAN) unit, i.e., mg of KOH needed to neutralize 1 gram of oil. It may be determined by titration according to ASTM D-664. Any acidic petroleum oil may be treated according to the present invention, for example, oils having an acid neutralization of about 0.5 mg KOH/g or greater.
The following examples illustrate the invention.